CHILD support, not the ex's "recreational" funds

With the "unadmirable" habits of my son's mother, is it possible that I can have the amount that I pay for child support minimized? For example: she's been 'training' in her current position for the last 2 years, and still is hardly earning any of her 'own' income, with the exception of this child support, of course. Yet, she hardly is home everynight until roughly 10 or 11 o'clock, and on the weekends, she's always out on her own. She pretty much drops him off to school, and then doesn't see him again at night before he goes to bed. Yes, my son resides w/her & her parents, but he is always home alone w/his grandparents. We are on 'rotating weekends', though when I call to talk to my son when he isn't with me, he's always at someone else's house where his mother has "dropped him off", because again, she's out. She even drops him off to my mother when I'm not around, and doesn't even advise me beforehand that she's doing so. The only way that I ever find these incidents out, is when my mom calls me to let me know that my son is with her. She even still will ask me for extra cash because she says that she's "broke". It's very irritating to me.

I feel that my "child support" is going more towards her "recreational" support, and I want to know that the amount that I pay (almost $900/mo) goes directly towards my son's needs, not hers.

Let the judge know that and indeed you may be able to get the payments reduced.